..some kind of digital recorder...
(this one is limited to clearance, but it's an idea of what's available)
ok, this may be a music store site, but they know recording!
Notebooks are worthless cause you have to sit and write. With a portable recorder, you can sit and have an adult refreshment and muse over your day's wanderings without so much as lifting a pen! They're also small enuf to carry on a bike. And if there's company around, even ask if anyone remembers what all those little town's names are you rode thru and forgot...
Mary aka Krashdragon